Preparing for Harvest: Do You Need Silage Inoculants?

Kirby Krogstad, Assistant Professor; Jason Hartschuh, Dairy Field Specialist; Dwight Roseler, Adjunct Faculty; and Maurice Eastridge, Professor, The Ohio State University

Introduction

Silage, whether it be corn, alfalfa, or some other crop, is a staple in dairy cattle rations. Silage can be fed to animals at nearly all ages, from post-weaning heifers to mature cows. High quality silage can promote efficient growth of replacement dairy cattle or efficient milk production of lactating dairy cows. As positive as high-quality silage can be, poor silage can be equally problematic. Whether the silage is of great or poor quality, you’re stuck with it for at least a year. As Kung and Muck (2017) stated, “…decisions made during the relatively few days a year spent on harvesting and silo filling can affect feeding value of the silage for the next year.” Investing time, energy, and resources to get silage harvested and stored right are resources well spent.

Creating high-quality silage is a product of multiple management decisions, such as harvest timing, chop length, packing density, and effective sealing, covering, or bagging of the silage. Selection and utilization of silage inoculants play an important supporting role in silage management. While inoculants don’t guarantee a perfect silage crop, they increase the probability of having a good silage crop, especially by mitigating dry matter losses during storage. Our goal is to introduce and describe important considerations when selecting microbial silage inoculants.

Silage Fermentation

Silage fermentation proceeds in stages (Figure 1). First, a silage is aerobic, meaning there is oxygen present. During this stage, plant respiration continues and aerobic bacteria are present. After the silage is covered and microbes begin their work, the oxygen is consumed and carbon dioxide is produced which begins to create an anaerobic environment. As the oxygen is depleted, sugars are degraded and anaerobic bacteria increase, which results in the production of acids that reduce silage pH, especially lactic acid. If these steps proceed as described, the silage will have a low pH, be at low risk for clostridium or other contaminants, and remain relatively stable, even for long periods of time and have better aerobic stability when the surface is exposed. Silage inoculants can shorten the first 4 phases of this process by aiding in acid production and pH decline.

Figure 1. Process of silage fermentation. Adapted from Jones et al., 2004.

Types of Inoculants

Inoculants aid silage in three key areas: enhance adequate fermentation, prevent clostridial fermentation, and enhance aerobic stability of silage at feed out.

The microbial species used in inoculants are categorized based on their lactic acid production: homolactic acid bacteria, heterolactic acid bacteria, and combination of both homo- and heterolactic acid bacteria. The distinction may seem superfluous, but the microbial metabolism is critical to the benefits of using an inoculant during silage production.

Homolactic acid bacteria are those that produce only lactic acid as an end-product of their metabolism. Lactobacillus plantarum and Enterococcus faecium are two such examples. Homolactic acid bacteria have long been used for microbial silage inoculants because they produce lactic acid which reduces the pH – a critical step in the ensiling process. Enhancing pH reduction is important in forages with less starch or sugar as these fuel acid production during ensiling. Alfalfa silage is a prime example; ensiling alfalfa silage with homolactic acid bacteria inoculants reduced the alfalfa silage pH by 0.3 units and increased lactic acid by 10 to 20% (Li et al., 2022). Similar results were obtained in a meta-analysis; homolactic acid bacteria inoculants reduced silage pH, increased lactic acid, and reduced yeasts and mold contaminants (Blajman et al., 2020).

Heterolactic acid bacteria produce a distinct fermentation pattern, greater acetate production being the most prominent change. Acetic acid increases by 20 to 78% when utilizing Lactobacillus buchneri in a microbial silage inoculant. Researchers have observed that lactic acid was reduced and pH was similar or marginally greater when adding L. Buchneri to silage, but yeast contamination was reduced and aerobic stability increased when utilizing this heterolactic acid bacteria (Kleinschmit and Kung, 2006, Schmidt and Kung, 2010). Thus, when using heterolactic acid bacteria, expect greater acetic acid, less lactic acid, and slightly greater pH than if using a homolactic acid bacteria inoculant.

Figure 2. Decision tree to aid in selection of microbial inoculants for silages fed to dairy cattle. Created in https://BioRender.com.

How to Choose

Choosing an inoculant depends on the goals of the silage management program, the challenges facing the silage program, or the forage type being ensiled.

If you’re ensiling alfalfa or grass (low in starch), homolactic acid silage inoculants are preferred as they rapidly reduce silage pH. The rapid pH reduction inhibits problematic bacteria, like Clostridium. Grain silages experience less benefit from homolactic acid silage inoculants because the sugar and starch content of the feed helps enhance fermentation to reduce pH. Homolactic acid bacteria generally don’t reduce pH in a well-fermented grain silage. Grain silage can benefit from a mixed or heterolactic acid silage inoculant because the increased acetic acid improves stability at feedout while reducing yeast or mold contamination. Mixed and heterolactic acid silage inoculants are beneficial if you’re expecting challenges that affect aerobic stability like greater dry matter at harvest, hot weather when feeding, feeding from multiple silage faces, not feeding enough silage from the silage face, or if you have to move the silage and re-ensile it. The decision tree in Figure 2 may be a helpful starting point when selecting your microbial silage inoculant.

Milk Production Responses

Improvements in silage fermentation alone have a dollar value but inoculated-silage also promotes greater milk production when fed to dairy cattle. This could occur in response to forage of greater nutritional value and by increasing dry matter intake. A 2026 research experiment demonstrated that cows fed corn silage inoculated with a mixed lactic acid bacteria inoculant produced 2.6 kg/d (5.7 lb/d) more milk than cows fed a non-inoculated corn silage (Niño de Guzmán et al., 2026). In a meta-analysis (a summary of 31 experiments), feeding inoculated silage increased milk yield by 0.37 kg/d (0.82 lb/d) (Oliveira et al., 2017).  These experiments demonstrate that microbial inoculation helps with both silage fermentation and the cow’s milk production.

Conclusions

Silage quality is important for dairy farm’s nutrition program, milk yield, animal health, and therefore can has considerable economic impact. Good silage management, including proper harvest timing, ensiling, storage, and feedout are nonnegotiable fundamentals when feeding silage. Silage inoculants play an important supporting role by reducing silage pH, increasing aerobic stability, and improving milk production. Using an inoculant typically is not an ‘if’ scenario, but a ‘which one’ proposition. When selecting a microbial silage inoculant, following our decision tree will be a useful starting point.